I built an 8 ft diameter light display made up of 7 segments, each using a 16 bit MCP23017 port expander.
Before I built the big guy, I built a table-top version about 16" in diameter, using the same port expanders at the same addresses. this was so I could program on the small model in my office while building the big model in my shop. I will use the exact same program when finished.
I would really like to be able to view the small model at the same time the big model is working, sort of like a "monitor". If I make a programming change on the small model, it gets reflected on the big one.
How can I do this? Can it be done with one Arduino (UNO in this case)? How do I resolve the addressing for the port expanders which only allow me 8 addresses from $20 to $27?
Can I somehow use one Arduino as a relay (ie as an I2C port) to the other without addressing conflicts?